The present invention relates to a compression self-ignition gasoline engine which comprises a fuel injector injecting fuel directly into a combustion chamber and proceeds a combustion by self-igniting mixture in the combustion chamber due to the piston compression operation.
It is known that a theoretical thermal efficiency is improved by varying the air-fuel ratio of mixture toward a lean side to decrease a pumping loss and by increasing a ratio of a specific heat of operation gas for the purpose of improving the thermal efficiency of a gasoline engine. However, a spark-ignition type internal combustion engine has a tendency that a combustion period is elongated by varying as the air-fuel ratio to the lean side, thereby degrading a combustion stability of the engine. That is, such a spark-ignition type internal combustion engine has a limitation of varying the air-fuel ratio to the lean side.
Japanese Patent Provisional Publication No. 7-332141 discloses a compression self-ignition internal combustion engine that is arranged to generate a pre-mixing compression self-ignition combustion. This is proposed in order to achieve the stable engine operation under the lean air-fuel ratio. Further, Japanese Patent Provisional Publication No. 11-182246 discloses an internal combustion engine that is arranged to increase the temperature in each cylinder by returning exhaust gas to an intake passage. This is proposed in order to improve the ignitability of fuel during the self-ignition combustion.
Although the latter proposed engine improves a problem of the former proposed engine that the ignitability of fuel during the self-ignition combustion should be improved, in some degree, it is further required to improve the ignitability.
It is an object of the present invention to improve the ignitability of a gasoline engine during the compression self-ignition combustion at a wider engine operation region without generating knocking.
A first aspect of the present invention resides in a compression self-ignition gasoline engine which comprises a stratifying device stratifying gas in a combustion chamber of the engine, a fuel injector directly injecting fuel in the combustion chamber and a controller connected to the stratifying device and the fuel injector. The controller controls the stratifying device to produce a high temperature gas layer of a high temperature gas and a low temperature gas layer of a low temperature gas in the combustion chamber. The controller controls the fuel injector to inject the fuel to both the high temperature gas layer and the low temperature gas layer.
Another aspect of the present invention resides in a compression self-ignition gasoline engine which comprises a stratifying device which stratifies gas in a combustion chamber of the engine and a fuel injecting which directly injects fuel in the combustion chamber. The stratifying device produces a high temperature gas layer of a high temperature gas and a low temperature gas layer of a low temperature gas in the combustion chamber. The fuel injector injects fuel to both the high temperature gas layer and the low temperature gas layer.